Replace inter-service _handlers dicts with declarative sx defquery/defaction

The inter-service data layer (fetch_data/call_action) was the least
structured part of the codebase — Python _handlers dicts with ad-hoc
param extraction scattered across 16 route files. This replaces them
with declarative .sx query/action definitions that make the entire
inter-service protocol self-describing and greppable.

Infrastructure:
- defquery/defaction special forms in the sx evaluator
- Query/action registry with load, lookup, and schema introspection
- Query executor using async_eval with I/O primitives
- Blueprint factories (create_data_blueprint/create_action_blueprint)
  with sx-first dispatch and Python fallback
- /internal/schema endpoint on every service
- parse-datetime and split-ids primitives for type coercion

Service extractions:
- LikesService (toggle, is_liked, liked_slugs, liked_ids)
- PageConfigService (ensure, get_by_container, get_by_id, get_batch, update)
- RelationsService (wraps module-level functions)
- AccountDataService (user_by_email, newsletters)
- CartItemsService, MarketDataService (raw SQLAlchemy lookups)

50 of 54 handlers converted to sx, 4 Python fallbacks remain
(ghost-sync/push-member, clear-cart-for-order, create-order).
Net: -1,383 lines Python, +251 lines modified.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/infrastructure/protocol_manifest.py

@@ -0,0 +1,58 @@
+"""Protocol manifest — aggregates /internal/schema from all services.
+
+Can be used as a CLI tool or imported for dev-mode inspection.
+
+Usage::
+
+    python -m shared.infrastructure.protocol_manifest
+"""
+
+from __future__ import annotations
+
+import asyncio
+import json
+from typing import Any
+
+from shared.infrastructure.data_client import fetch_data
+
+
+# Service names that have inter-service protocols
+_SERVICES = [
+    "blog", "market", "cart", "events", "account",
+    "likes", "relations", "orders",
+]
+
+
+async def fetch_service_schema(service: str) -> dict[str, Any] | None:
+    """Fetch /internal/schema from a single service."""
+    try:
+        from shared.infrastructure.urls import service_url
+        import aiohttp
+        url = service_url(service, "/internal/schema")
+        async with aiohttp.ClientSession() as session:
+            async with session.get(url, timeout=aiohttp.ClientTimeout(total=3)) as resp:
+                if resp.status == 200:
+                    return await resp.json()
+    except Exception:
+        return None
+    return None
+
+
+async def generate_manifest() -> dict[str, Any]:
+    """Fetch schemas from all services and produce a unified protocol map."""
+    results = await asyncio.gather(
+        *(fetch_service_schema(s) for s in _SERVICES),
+        return_exceptions=True,
+    )
+    manifest = {"services": {}}
+    for service, result in zip(_SERVICES, results):
+        if isinstance(result, dict):
+            manifest["services"][service] = result
+        else:
+            manifest["services"][service] = {"error": str(result) if isinstance(result, Exception) else "unavailable"}
+    return manifest
+
+
+if __name__ == "__main__":
+    m = asyncio.run(generate_manifest())
+    print(json.dumps(m, indent=2))